Another botched distributor installation corrected

[Duke W.]

... '65 L-78 owned by a friend of a friend ('67 L-71 Duntov award). The engine was rebuilt ten years ago, and the owner has only driven it 400 miles since then. It had a severe case of "trailer-hitching" at 1500-2000 revs, light load and was not at all pleasant to drive. We removed the top distributor shield and I immediately saw a problem. The cap window was rotated to the left rather than being near normal to engine centerline, and the plug wires were installed one position CCW from proper indexing so #1 was to the left (as viewed from the driver's seat) of the cap window rather than to the right (passenger side). I figured there were likely other issues and suggested that we pull the distributor for a "blueprint overhaul" the following week, which was yesterday.

After indexing the crank at 10 deg. TDC #1 compression stroke we pulled the distributor, and I lost the first bet because the gear was actually properly indexed with the dimple pointing the same direction as the rotor tip. My bet was that it would be 180 degrees out. One .030" shim was installed and end play was .065". The installed VAC was a 8" B28, and we had a 12" B26, but it was out of spec requiring 14" to pull to the limit, so we retained the B28 . Fortunately the shaft and housing bushings were in good shape, and the only significant problem was that the pickup coil pigtail wires had been spliced and wrapped with tape. One had a solder ball on the splice and the other was just twisted together. Bubba had definitely been there. Fortunately my buddy can solder so he took care of that with a nice solder and shrink tubing job while the owner and I cleaned parts.

Assembly went smoothly after filling the grease well with 1960954 Delco Distributor and Stater Motor lubricant that we also used on the tach drive gears. We added two .030" shims before installing the gear and end play checked out at .006".

After having to tweak the oil pump drive a couple of times with my "special tool" (a Home Depot paint mixing stick) the distributor seated and I rotated the base to line up the stationary pole pieces with the rotating pole pieces. We installed the cap and reindexed the wires one position CW that put #1 wire along the right (passenger side) of the cap window, and it was time to start.

The carburetor was some replacement that has a non-functional electric choke (The owner has an overhauled original and that's his next project). After a couple of backfires with small fireballs, I was beginning to worry. My reputation was on the line, so I manually closed the choke, and it started, but ran pretty ragged. Once the engine warmed up somewhat I was able to set hot idle speed and initial timing checked out right at 10 degrees with zero scatter, so we locked down the distributor, installed the air cleaner, and went for a test drive.

The trailer hitching was gone and the engine ran smooth as silk. The owner couldn't believe the difference. I wanted to check the entire spark advance map and try some lighter centrifugal springs, but we were getting short of time and agree to do that job maybe next Saturday.

I have no doubt that there are many more screwed up distributor installations out there. I've been running across them for over 55 years.

Duke

[Mark E.]

Re: Another botched distributor installation corrected

What do you think caused the "trailer hitching"? I'm guessing the excessive end play? Or initial timing?

Although it may cause issues with the tach drive cable and clearance for the VAC, a distributor can be indexed and installed in any orientation without affecting performance.

[Duke W.]

Re: Another botched distributor installation corrected

That's a common myth and maybe why so many are screwed up. The gear has 13 teeth so each position rotates the shaft about 28 degrees. The cap has eight positions, which is 45 degrees separation, so not all wire indexing schemes line up the rotor tip with the cap terminal.

Lean mixtures are more difficult to ignite than rich mixtures, so if the rotor tip and cap terminals are significantly out of alignment a lot of spark energy is dissipated in the big gap between the rotor and cap terminals leaving insufficient energy to jump the gap at the spark plug.

The problem was also exacerbated on this engine having too much initial timing when I first checked it so jerkiness was the result of two problems.

Excess end play causes spark scatter that creates slightly different torque on the crankshaft among the various cylinders. Most never noticedthe slight roughness this causes until the end play is shimmed up to the 2 to 7 thou spec. I'm my experience and some others shimming up excess end play yields a smoother engine.

Duke

[Frank D.]

Re: Another botched distributor installation corrected

Seems to be a recurring problem, particularly with novices, who just yank the distributor out without marking anything for re-stabbing it, OR can't find compression stroke TDC on #1 OR disturb the engine with the distributor out. Next thing you know they are doing musical chairs with the plug wires at the distributor cap towers to get things running.

I find Lars method of "walking" the rotor into the proper position less frustrating than the paint stick or screwdriver down the distributor hole.
Its great that you helped out a fellow onwer that was clearly out of his depth !

[Mark E.]

Re: Another botched distributor installation corrected

That's a common myth and maybe why so many are screwed up. The gear has 13 teeth so each position rotates the shaft about 28 degrees. The cap has eight positions, which is 45 degrees separation, so not all wire indexing schemes line up the rotor tip with the cap terminal. Duke

I'm not getting it Duke. If the distributor shaft is indexed one tooth clockwise, and the distributor housing is turned clockwise the same amount (almost 28*, as you say) how does this change the timing of the engine? Or the relative position of the rotor tip and cap terminal?

[William F.]

Re: Another botched distributor installation corrected

If you're removing a distributor from a car that has been running, not trying to set up a distributor after an engine rebuild, can't you just mark position of rotor, distibutor body as there are to each other and to a mark on engine block or valve cover and make sure they all line up when you but distributor back in rather than worrying about where crank timing mark is? Believe john Hinkley referenced this in on of his articles in corvette Forum.

[Duke W.]

Re: Another botched distributor installation corrected

I'm not getting it Duke. If the distributor shaft is indexed one tooth clockwise, and the distributor housing is turned clockwise the same amount (almost 28*, as you say) how does this change the timing of the engine? Or the relative position of the rotor tip and cap terminal?

Assume that the rotor tip is aligned with the #1 terminal in the cap with the wires in the correct cap recepacles. Now move the shaft once tooth CCW, which is 13 degrees. So to retain the same initial timing you have to move the dist housing 13 degrees CCW. But the terminals are 45 deg. apart, so now the rotor is misaligned with the #1 terminal by 45-28 = 17 degrees.

There were other issues. We weren't sure if the pickup coil wires were installed properly in the connector. The green stripe in one wire was virtually faded away. The polarity may have been reversed, but I don't know how that would effect engine operation. We had a spare TI distributor and the CSM wiring diagram for reference and made a decision that was apparently correct because it's now a perfect running engine.

Duke

[Stephen L.]

Re: Another botched distributor installation corrected

The relationship of the piston and valve train must be considered when the distributor is off by 1 tooth relative to the rotor position and cap.....

[Frank D.]

Re: Another botched distributor installation corrected

If you're removing a distributor from a car that has been running, not trying to set up a distributor after an engine rebuild, can't you just mark position of rotor, distibutor body as there are to each other and to a mark on engine block or valve cover and make sure they all line up when you but distributor back in rather than worrying about where crank timing mark is? Believe john Hinkley referenced this in on of his articles in corvette Forum.

Absolutely - and the way I usually do it on an engine I KNOW had the distributor stabbed correctly beforehand; of course you can't disturb the engine while the distributor is out or its a whole new ball game.

[Tom P.]

Re: Another botched distributor installation corrected

Seems to be a recurring problem, particularly with novices, who just yank the distributor out without marking anything for re-stabbing it, OR can't find compression stroke TDC on #1 OR disturb the engine with the distributor out. Next thing you know they are doing musical chairs with the plug wires at the distributor cap towers to get things running.

I find Lars method of "walking" the rotor into the proper position less frustrating than the paint stick or screwdriver down the distributor hole.
Its great that you helped out a fellow onwer that was clearly out of his depth !

Frank,
With that thought in mind, I made this "tool" many years ago so that I could align the oil pump shaft to the needed position to allow the distributor to drop right in. And it also is my oil priming tool. It's an old, junk alum housing point type dist with the upper end turned down to fit a 3/8 drill and the teeth ground off of the gear.
These old distributors can be picked up for anything from free to $5.

[Frank D.]

Re: Another botched distributor installation corrected

Clever Tom.

[Duke W.]

Re: Another botched distributor installation corrected

If you're removing a distributor from a car that has been running, not trying to set up a distributor after an engine rebuild, can't you just mark position of rotor, distibutor body as there are to each other and to a mark on engine block or valve cover and make sure they all line up when you but distributor back in rather than worrying about where crank timing mark is? Believe john Hinkley referenced this in on of his articles in corvette Forum.

What if the gear is not indexed properly? You don't know until you remove the distributor, and if it's 180 out your marks don't mean squat. Same if the gear is not indexed properly on the cam. And what if you wash off any marks from cleaning all the parts. I learned the hard way 55 years ago about bad distributor installations. The "experts" I consulted were clueless. I finally figured it out on my own and what works every time for me without any guesswork other than tweaking the oil pump drive shaft. Once it's lined up and the distributor seats I KNOW FOR SURE that initial timing is within a degree or two of where I set the balancer notch on the timing tab.

To set the crank position just put the car it top gear and bump it forward until the notch is where you want it on the tab and the rotor is pointing at the terminal that holds the #1 plug wire. Of course this won't work on an automatic. I've never pulled the dist. out of an automatic, but you can probably reasonably line up the balancer notch by bumping the starter. If the engine has a center bolt on the balancer you can rotate the crank with a socket wrench.

Of course there are other ways to do the job. I don't consider them to be as "sure fire" as my method, but everyone is free to use whatever works best for them. I just offer suggestions based on my experience.

Duke

[Mark E.]

Re: Another botched distributor installation corrected

Assume that the rotor tip is aligned with the #1 terminal in the cap with the wires in the correct cap recepacles. Now move the shaft once tooth CCW, which is 13 degrees. So to retain the same initial timing you have to move the dist housing 13 degrees CCW. But the terminals are 45 deg. apart, so now the rotor is misaligned with the #1 terminal by 45-28 = 17 degrees.

There were other issues. We weren't sure if the pickup coil wires were installed properly in the connector. The green stripe in one wire was virtually faded away. The polarity may have been reversed, but I don't know how that would effect engine operation. We had a spare TI distributor and the CSM wiring diagram for reference and made a decision that was apparently correct because it's now a perfect running engine.

Duke

If the shaft is reclocked one tooth CCW (almost 28 camshaft degrees as you said initially) and then the housing is also moved 28 degrees CCW, ignition timing is not affected. All relavent components (points, distributor cam, rotor, cap) are in the same relative position.

So I can orient the distributor in any position I want (barring clearance problems and tach cable bends).

Maybe you're talking about reclocking the position of the ignition cables in the cap? Yes, that will cause issues.

[Gary C.]

Re: Another botched distributor installation corrected

If the shaft is moved one tooth CCW (which is 13 deg), the rotor also moves 13 deg CCW as well as the point cam/rotating pole piece (TI), they are linked together. Then to get correct timing, you move the housing 13 deg CCW and the cap and points plate/stationary pole piece (TI) goes along with the housing 13 deg CCW and all back into timing, nothing out of place in terms of timing. Obviously, spark plug wires go along with the cap movement.

The issue with doing this on Corvettes like Mark's 70 and my 69 & 71 is now the VAC is now moved 13 deg CCW and probably will hit the ignition shield/supports and the angle for the tach drive cable has this 13 deg CCW bend as well. Without these two (ignition shield/supports and tach drive) it does not matter which way you install the distributor gear, you can always time the distributor, the net effect is where the VAC points.

[Mark E.]

Re: Another botched distributor installation corrected

If the shaft is moved one tooth CCW (which is 13 deg), the rotor also moves 13 deg CCW as well as the point cam/rotating pole piece (TI), they are linked together. Then to get correct timing, you move the housing 13 deg CCW and the cap and points plate/stationary pole piece (TI) goes along with the housing 13 deg CCW and all back into timing, nothing out of place in terms of timing. Obviously, spark plug wires go along with the cap movement.

The issue with doing this on Corvettes like Mark's 70 and my 69 & 71 is now the VAC is now moved 13 deg CCW and probably will hit the ignition shield/supports and the angle for the tach drive cable has this 13 deg CCW bend as well. Without these two (ignition shield/supports and tach drive) it does not matter which way you install the distributor gear, you can always time the distributor, the net effect is where the VAC points.

That's right. But rotating the shaft one distributor gear tooth changes timing by 360*/13 teeth = 27+ camshaft degrees or 55+ crank degrees.

I believe Duke may have been talking about the problems associated with re-clocking the ignition wires in the cap.